Abstract: The associative kinetics of one coal soluble constituent; pyridine insoluble (PI) and carbon disulfide-N-methyl-2-pyrrolidinone (CS2/NMP) mixed solvent soluble was investigated. It is clarified that the aggregation of PI molecules in NMP solution is a reaction controlled mechanism. A two-step kinetic process is provided, which are the formation of elemental aggregates and their clustering. The associative rate for the aggregation at different holding temperatures and solvents were determined, and the rate constants follow the Arrhenius equation. The activation energy of the aggregation of PI molecules in NMP solution is 73.3 kJ/mol and 21.6 kJ/mol for the first and the second step, respectively. The effect of temperature on the aggregation rate is remarkable, and the aggregation rate increases with increasing temperature. The aggregation rate of PI molecules in CS2/NMP mixed solvent is more quickly than that in NMP due to the higher diffusibility (mobility) of PI-1 molecules in the mixed solvent. The aggregation mechanism of PI molecules in solution was also discussed.